1. Field of the Invention
The present invention relates to a magneto-resistance effect element and a thin-film magnetic head.
2. Description of the Related Art
Magnetic disk drives employ a thin-film magnetic head having a magneto-resistance effect element (MR element) for reading magnetic signals. In recent years, efforts have been made to design magnetic disk drives for higher recording densities, and accordingly there are growing demands for thin-film magnetic heads, particularly magneto-resistance effect elements, which satisfy higher-sensitivity and higher-output requirements.
A CIP-GMR (Current in Plane-Giant Magneto-resistance) element which is a giant magneto-resistance effect element having a nonmagnetic layer between ferromagnetic layers and passing a sensing current in parallel to a layer surface, has been conventionally developed as a reproducing element in a thin-film magnetic head. On the other hand, a magnetic head that uses a TMR (Tunnel Magneto-resistance) element which has an insulation layer instead of the nonmagnetic layer as an intermediate layer and which passes a sensing current perpendicular to a layer surface, has also been developed in order to achieve higher densification. Furthermore, a magnetic head that uses a CPP (Current Perpendicular to Plane)-GMR element which is a GMR element having a nonmagnetic layer as the intermediate layer and passing a sensing current perpendicular to the layer surface similar to the TMR element, has also been developed. CPP-GMR element has an advantage of having low resistance in comparison with the TMR element and having higher output in a narrower track width than the CIP-GMR element.
An ordinary GMR element is in the cylindrical shape of a desired size, and has a structure interposing a non-magnetic spacer layer between a pinned layer which is a ferromagnetic layer in which the magnetization direction is fixed a and a free layer which is a ferromagnetic layer in which the magnetization direction varies according to an external magnetic field. Such a GMR element is also referred to as a spin valve film (SV film). The upper and lower ends of the GMR element are provided with a cap layer and a buffer layer, respectively. The cap layer, the GMR element, and the buffer layer are interposed between the upper shield layer and the lower shield layer. In the case of the CPP-GMR element, the upper shield layer and the lower shield layer function as an electrode, respectively, and a sense current flows in a direction orthogonal to the layer surface.
The spacer layer of a conventional CPP-GMR element has been most commonly comprised of Cu that is about 3.0 nm in thickness. However, in the CPP-GMR element having a spacer layer comprising Cu, since Cu has a low resistance, the sheet resistance (RA value) is low, and, for example, it is 0.07 Ω·μm2, and the MR ratio is also low, and it is below about 4%. In this CPP-GMR element, to obtain a sufficient output voltage, it has been necessary to operate the element at a high current density. When the element is operated at the high current density, an electro-migration phenomenon occurs in which a metallic atom colliding with an electron migrates, and there is a fear that the magneto-resistance effect element will be destroyed by the migration of the atom and its life span becomes extremely short. Further, when the element is operated at the high current density, an output noise caused by a spin transfer torque occurs, and a practical problem arises.
To increase the RA value of the CPP-GMR element, a confined-current-path type magneto-resistance effect element a has been proposed, in which a non-current portion is provided inside the spacer layer and the current is allowed to flow in a direction vertical to the layer surface by passing through only certain portions inside the spacer layer. In the confined-current-path type magneto-resistance effect element, the resistance of the spacer layer can be substantially high, thereby the RA value can be high. However, such a confined-current-path type magneto-resistance effect element has been difficult to manufacture, and it was extremely difficult to form the element at a high dimensional accuracy so as to be able to obtain desired performance.
Hence, as a method for making the RA value of the CPP-GMR element high by a technique other than confining the current path, an example described below is available.
Japanese Patent Laid-Open No. 2006-99872 proposes a magneto-resistance effect element, in which the spacer layer is of a three layer structure comprising a first boundary surface layer, an electrically conductive layer, and a second boundary surface layer. The first and second boundary surface layers comprise CuAu, CuPd, CuPt, CuRu, CuNi, or CuPh, and the electrically conductive layer comprises Au, Pt, Ni, Pd, Cr, CuPd, CuPt, CuNi, or CuCr.
Japanese Patent Laid-Open No. 2003-8102 proposes a magneto-resistance effect element provided with a resistance adjusting layer adjacent to the spacer layer, in which the number of electrically conductive carriers is equal to or below 1022 coulomb/cm3. The spacer layer comprises Cu, Au, Ag, Ru, Ir, Pd, Cr, Mg, Al, Rh, Pt, or the like. The resistance adjusting layer comprises a semiconductor or a half metal, and is based on graphite, As, Sb, Bi, HgTe, HgSe, CoSi, (Co1-x, Fex)Si, (Cox-1, Nix)Si, (Cox-1, Mnx)Si, (Cox-1, Crx)Si, FeS, C, Si, Ge, AlN, GaN, InN, AlP, AlAs, AlSb, GaP, GaAs, GaSb, InP, InAs, InSb, ZnO, β-ZnS, ZnSe, ZnTe, CdS, CdTe, HgTe, α-SiC, β-SiC, PbS, PbSe, PbTe, SnTe, CuInSe2, FeSi2.43, β-FeSi2, MnSi1.72, CrSi2, (Cr1-xMnx)Si2, Mg2Si, BaSi2, ReSi1.75, RuSi3, OsSi2, or Ir3Si5.
According to the above described two Patent Documents, a structure is disclosed in which the spacer layer is substantially made into a multi-layer structure, thereby attempting to improve the MR ratio to some degree as compared with the spacer layer having a Cu single layer. In these Patent Documents, although the matter that is used as the material for each layer is illustrated, it is just a listing of the different kinds of matter, and there is no comparison or study of the individual matter. That is, a specific proposal for the most appropriate material to improve the MR ratio is not submitted.